DEBORAH SMITH SCIENCE EDITOR

THIS year's El Nino event has ramped up during spring, with water temperatures in some regions of the tropical Pacific Ocean reaching up to six degrees above normal.

The phenomenon is expected to persist throughout summer, increasing the chance of drier conditions for eastern Australia.

David Jones, head of climate analysis at the Bureau of Meteorology, said every El Nino was different and this one had had a ''stop-start'' beginning in winter.

''But it has really cranked up a gear,'' he said. ''It has gone from being marginal into what is a significant El Nino event.''

The central Pacific has heated up to a level not observed since the El Nino of 2002, with a huge wave of warm water moving eastward, bringing the welcome prospect of rain for the west of the US. On average, water surface temperatures near the equator are two degrees above normal, but the temperature of some waters deeper down are six degrees higher than usual, the bureau said.

Dr Jones said the fact this year's event had strengthened in spring, rather than earlier, meant that its impact on rainfall across the continent had been weak during winter. ''When people look back at this event I think it will be realised we've been pretty lucky.''

Drier than normal conditions, however, are now expected for south-east Queensland and much of NSW until at least the end of January.

Bill Patzert, a NASA oceanographer, said it was good news that El Nino had picked up steam. ''In the American west where we are struggling under serious drought conditions, this charge by El Nino is a pleasant surprise, upping the odds for much-needed rain and an above-normal winter snowpack.''

El Nino events occur about every two to five years and the last ones, in 2002 and 2006, were associated with very dry conditions in Australia.